When packets are transmitted in a mobile communication system, the packets are transmitted via a wireless channel and thus distortion of a signal may occur in the transmission process. In order to enable a receiver to accurately receive the signal, channel information should be acquired such that the distortion of the transmitted signal is corrected by the channel information. In order to acquire the channel information, a method for transmitting a signal known to both a transmitter and a receiver and acquiring channel information from the distortion degree of the signal when the signal is received via a channel is mainly used. At this time, the signal known to both the transmitter and the receiver is referred to as a pilot signal or a reference signal (RS).
Recently, in most mobile communication systems, when packets are transmitted, a method for improving data transmission/reception efficiency using multiple transmission antennas and multiple reception antennas has been used, unlike the related art using one transmission antenna and one reception antenna. The transmitter or the receiver of the mobile communication system uses multiple antennas so as to increase capacity or improve performance. If data is transmitted or received using multiple antennas, in order to accurately receive the signal, the channel statuses between the transmission antennas and the reception antennas should be acquired from the respective RSs of the transmission antennas.
In a mobile communication system, RSs may be largely divided into two RSs according to their purposes: a common-RS for acquiring channel information and an RS used for data demodulation. The former is used for enabling a User Equipment (UE) to acquire downlink channel information. Therefore, the common-RS should be transmitted in a wideband, and even a UE which does not downlink data in a specific subframe can receive and measure this RS. In addition, the common-RS is also used for measurement for handover or the like. The latter is an RS which is sent together with resources when a base station (eNB) sends downlink data. The UE may receive this RS so as to perform channel estimation and demodulate the data. This RS should be transmitted in a region in which data is transmitted.
FIG. 1 is a view showing a downlink frame structure of Long Term Evolution (LTE).
The basic frame structure is the LTE structure shown in FIG. 1. A Physical Downlink Control Channel (PDCCH) region in which a control signal is transmitted and a Physical Downlink Shared Channel (PDSCH) region in which data is transmitted are Time-Division-Multiplexed (TDM) in every subframe. When the eNB transmits a signal in downlink, the PDCCH is transmitted first and the PDSCH is then transmitted. The PDCCH includes information about the PDSCH. UEs acquire information indicating in which region or with what Modulation Coding Scheme (MCS) level their data is transmitted, by decoding the PDCCH. When the eNB transmits the PDCCH, information about the data of several UEs is transmitted. At this time, the eNB forms the PDCCH using the ID of each of the UEs. Each of the UEs decodes the PDCCH using its UE ID.
In a cellular communication system in which one eNB controls a plurality of UEs, the plurality of UEs receives control information via a downlink control channel transmitted from the eNB. At this time, since the number of PDCCHs which can be transmitted by the eNB at once is limited, different PDCCHs are not allocated to the UEs in advance, but the eNB transmits the control signal to any UE via any PDCCH. Each of the UEs checks whether the control information transmitted via the PDCCH corresponds to the UE, using the UE ID included in the PDCCH. At this time, each of the UEs decodes a plurality of PDCCHs (or a plurality of possible PDCCH formats), receives the control information of the PDCCH if there is a PDCCH corresponding to the UE, and performs an operation.
When packets are transmitted in a mobile communication system, the packets are transmitted via a wireless channel and thus distortion of a signal may occur in the transmission process. In order to enable a receiver to accurately receive the signal, channel information should be acquired such that the distortion of the transmitted signal is corrected by the channel information. In order to acquire the channel information, a method for transmitting a signal known to both a transmitter and a receiver and acquiring channel information from the distortion degree of the signal when the signal is received via a channel is mainly used. At this time, the signal known to both the transmitter and the receiver is referred to as a pilot signal or a reference signal (RS).
Recently, in most mobile communication systems, when packets are transmitted, a method for improving data transmission/reception efficiency using multiple transmission antennas and multiple reception antennas has been used, unlike the related art using one transmission antenna and one reception antenna. The transmitter or the receiver of the mobile communication system uses multiple antennas so as to increase capacity or improve performance. If data is transmitted or received using multiple antennas, in order to accurately receive the signal, the channel statuses between the transmission antennas and the reception antennas should be acquired from the respective RSs of the transmission antennas.
In a mobile communication system, RSs may be largely divided into two RSs according to their purposes: a common-RS for acquiring channel information and an RS used for data demodulation. The former is used for enabling a User Equipment (UE) to acquire downlink channel information. Therefore, the common-RS should be transmitted in a wideband, and even a UE which does not downlink data in a specific subframe can receive and measure this RS. In addition, the common-RS is also used for measurement for handover or the like. The latter is an RS which is sent together with resources when a base station (eNB) sends downlink data. The UE may receive this RS so as to perform channel estimation and demodulate the data. This RS should be transmitted in a region in which data is transmitted.
FIG. 1 is a view showing a downlink frame structure of Long Term Evolution (LTE).
The basic frame structure is the LTE structure shown in FIG. 1. A Physical Downlink Control Channel (PDCCH) region in which a control signal is transmitted and a Physical Downlink Shared Channel (PDSCH) region in which data is transmitted are Time-Division-Multiplexed (TDM) in every subframe. When the eNB transmits a signal in downlink, the PDCCH is transmitted first and the PDSCH is then transmitted. The PDCCH includes information about the PDSCH. UEs acquire information indicating in which region or with what Modulation Coding Scheme (MCS) level their data is transmitted, by decoding the PDCCH. When the eNB transmits the PDCCH, information about the data of several UEs is transmitted. At this time, the eNB forms the PDCCH using the ID of each of the UEs. Each of the UEs decodes the PDCCH using its UE ID.
In a cellular communication system in which one eNB controls a plurality of UEs, the plurality of UEs receives control information via a downlink control channel transmitted from the eNB. At this time, since the number of PDCCHs which can be transmitted by the eNB at once is limited, different PDCCHs are not allocated to the UEs in advance, but the eNB transmits the control signal to any UE via any PDCCH. Each of the UEs checks whether the control information transmitted via the PDCCH corresponds to the UE, using the UE ID included in the PDCCH. At this time, each of the UEs decodes a plurality of PDCCHs (or a plurality of possible PDCCH formats), receives the control information of the PDCCH if there is a PDCCH corresponding to the UE, and performs an operation.